Why does Google Structured Data Testing Tool show errors?

WPSSO Core provides meta tags for webpages and Schema JSON-LD markup (WebSite, Person, and Organization) for the home page. The Google Structured Data Testing Tool checks most of these meta tag values, along with Schema / Microdata / RDFa markup, which may be included throughout your theme templates. If the Google testing tool shows an error, click on the error to see where in your webpage the incorrect markup is located. All WPSSO meta tags and Schema JSON-LD markup is located in the webpage head section, clearly indicated by begin / end markers (using HTML comments and/or HTML tags).